Grease composition for lubrication



patented duty 14, rear GREASE COIVHOSHTHGN FOR LUBRIIGATKON AlanBeerbower, Kenilworth, and old if. Morway, Rahway, N. 3., assignors toStandard Oil Development Company, a corporation of Dela- WHITE NoDrawing. Application February Serial No. 257,206

1 Claim.

The present invention relates to an improved grease composition forlubrication and to methods for preparing the same.

Grease compositions are prepared by adding metallic soaps to lubricatingoils, especially the soaps of those metals which cause the oil to gel.Of these metals, those of the first and second groups of the periodictable of elements are the most important, particularly sodium,potassium, calcium and barium. These may be used together or separatelyor they may be mixed with other metal compounds, particularly aluminum.1

The various soaps are used for different purposes as is well known inthe arts; for example, soda or potash soaps are preferred for hightemperature service and form the so-called fibrous greases, while limeand barium soaps are used for producing water resistant greases. Thequality of the greases is determined in the first instance bythe'particular soaps employed, but a considerable variation may beobtained by varying the amount of the soap and, for certain purposes, ithas been proposed to provide a slight excess offree alkali; for otherpurposes, a slight excess of free acid is preferred in the finalcomposition. The excess in either case is generally ouim small, usuallybelow about 1% and often only the smallest traces are suiiicient toproduce a considerable change in the structure of the grease, making itsuitable for one or another type of lubrication Lubricating greases,like oils, are subject to deterioration by oxidation. The deteriorationis slow but it results in the formation of partial oxidation productswhich appear to accelerate oxidation and deterioration until crustswhich are of no lubricating value are formed. The accumulation of thecrusty material gradually prevents proper lubrication by the unoxidizedportion of the grease. This deterioration is also catalyzed by variousmetallic surfaces and metallic ingredients, and particularly is itaffected by copper containing metals such as brass. Greases of all ofthe types mentioned above, whether containing traces of free acid orfree alkali, are subject to this type of decomposition and, likelubricating oils, the deterioration may to some extent be checked by theaddition-of inhibiting agents of which the best known are the aromatichydroxy and amine compounds.

It has been found that the choice of the inhibitor is particularlyafiected by whether the grease is one containing'a trace of free acid orfree alkali. Briefly, it has been found that when using greasescontaining free acid, the phenolic inhibitors are as a class markedlysuperior to the amino compounds and, on the other hand, when usingalkaline greases, that is to say those containing free alkali, the aminocompounds are greatly to be preferred to the phenolic materials. Noreason is known for this particular efiect, but it is believed that thefree acid present reacts quite rapidly with the free amine and in thesame way, a free alkali reacts quite rapidly with phenol and in this waythe inhibitors are rapidly removed if they are chosen in this way. Onthe other hand, no reaction takes place between the amine and thealkali, and any reaction which might possibly take place between thephenol and the acid is so slow as to be negligible. However this may be,the fundamental efiect on which the present applicants rely is theirdiscovery that phenolic inhibitors are much more efiective in greasewhich contain free acid and, on the other hand, amino compounds arelikewise much more effective in greases containing free alkali.

The grease may be made up of various fats or fatty oils, such as tallow,stea-rine, stearic acid,

' vegetable oils, marine oils and the various mixed fats obtainedtherefrom, and also from rosin, naphthenic acids or synthetic acids, forexample those obtained by the oxidation of highly purified oils, waxes,deoiled petrolatum and the like. The amount of the soap or soap mixturesused in the oil may, as indicated before, vary considerably say from 5to 10% to as much as 40 to 50% of the total mixture. As is well known inthe art, relatively small amounts of the soap produce low meltinggreases whereas larger amounts, up to 30, 40 or 50%, produce increasedhardness and raise the melting point.

Among the phenolic inhibitors which are used in connection with thepresent grease compositions, containing an excess of free acid, the mostimportant ones are alpha and beta naphthols, variou cresols and otheralkylated phenolic materials, dihydroxy and .polyhydroxy aromaticscontaining single or condensed rings, and also other compounds such asnitro phenols, halo phenols, guaiacol, eugenol and the like. Thephenolic inhibitors specifically mentioned are the ones preferred, butit may be stated as a generalrule that the phenolic materials as a classare quite eflfective for the present purposes and they are particularlyefiective in the presence'of free acids, whereas they are much lesseffective in the presence of free alkali.

Among the amino compounds which are found to be particularly effectivein grease compositions may be includedalpha. and beta naphthylamines,the substituted naphthylamines such as phenyl alpha and phenyl beta.naphthylamine, various cresyl amines, halo and nitro amines, variousdiamines such as phenylene diamines' or naphthalene diamine,diphenylamine and the like.

Here again it can be stated as a general rule that classes mentionedabove may be as little as .10%

or even less, and are used in less than 1% concentrations in the presentcase. In the specific choice of an. inhibitor for a grease, many factorsmust be taken into consideration. Some inhibitors are much moreeffective than others. The amount and the kind of soaps also have aprofound effect in the life of the grease and the oil also has a minoreffect so that all of these factors must be taken into account.Nevertheless, for the same basic grease formula, i. e.,.

greases made from the same oiland soap in the same proportions, it willbe found that the amino inhibitors as aclass are superior to thephenolic inhibitors where free alkali is present and vice versa wherefree acid is present.

The present greases may contain in addition to the ingredients mentionedabove, the various others which are employed in the grease making artfor specific purposes. It is usually the case to prepare soda and potashgrease in the absence of water whereas lime or barium greases usuallycontain about 1% of water. Glycerine or glycols may be present or absentdependingon the particular quality desired and among the other materialsorganic thickeners such as polybutylene waxes, for example, petrolatum,inorganic fillers,

tion of the inhibiting compounds.

EXAMPLE I The test used to establish the oxidation stability v of ourgreases is that developed by Wright and Lutz, described in ProductEngineering, vol. '7, pp. 210-13 '(1936). The apparatus consists of apressure-tight bomb fitted with an accurate gauge, and five smallglassdishes of standard size and shape. These dishes are loaded with thegrease to be tested and a catalyst, which may be any metal desired inthe form of a sheet or a fine powder. This catalyst serves the doublepurpose of imitating conditions in'a bearing and decreasing the timerequired for the test. We use a thin sheet of brass cut to fit the dish,or, no catalyst for very unstable greases. The filled dishes are placedin a suitable rack, and the whole sealed into the bomb. The bomb is thenflushed thoroughly with oxygen, filled to a suitable pressure, andplaced in an oil bath at 175 F. After temperature equilibrium isestablished, the pressure is adjusted to 110 lbs/sq. in. Readings aretaken of the pressure at two hour intervals.

The pressure is found to drop slowly at first, eight to twenty hoursbeing required for one pound loss, but suddenly the rate increases toseveral pounds every two hours. The time elapsed prior to the rapidincrease in oxygen absorption is called the life of the grease.

A ball bearing grease made from a Mid-Continent oil of 200 SayboltUniversal seconds at 100 F., 14% of sodium stearate, and /2% of aluminumstearate, with 0.1% free stearic acid, was tested with 0.1% each of thefollowing antioxidants:

Susceptibility of soda-aluminum grease Antioxidant NonePhenyl-a-naphthylamino. Phenyl-B-naphthylamine Guaiacol P-cresol .1

. EXAMPLE II Another grease, made with thesame oil, but

containing 21.25% sodium stearate, 2.75% barium stearate and 0.14% freesodium hydroxide gave the following results:

Susceptibility of soda-barium grease Antioxidant Life Hours In this casethe amine is superior although the guaiacol is fairly good.

EXAMPLE III A third grease prepared with a similar oil and containing15.5% sodium soapand 3.0% calcium soap of tallow, with 0.60% free sodiumhydroxide, gave the following results with 0.1% of antioxidants:

Susceptibility of soda-calcium grease Antioxidant Life Hours None 136Phenyl-a-naphthylamine 312 Guaiacol 174 Here again the amine is superiorto the phenol in the alkaline grease.

EXAMPLE IV A low temperature cup grease made from transformer oil and10% of calciumsoap of lard oil, containing excess free lime was testedwith 0.1% of inhibitors of both types.

Susceptibility of cup grease Antioxidant Life Hours None 4 Guaiacol 54Phenyl-a-naphthylamine 75 The present invention is not limited to anytheory of the action of the inhibiting compounds tion a small amount ofguaiacol.

ALAN BEERBOWER. ARNOLD J. MORWAY.

